The Info List - Dual Coupling

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Different types of railroad rolling stock have different couplers depending on the purpose and type of equipment being used and its intended destination. European rolling stock tend to use buffers and chain couplers while American rolling stock uses a Janney coupler
Janney coupler
or "knuckle coupler". These are incompatible with each other, but where some railroads have obtained older, less expensive used rolling stock from different countries or regions, instead of having to standardize on one form of coupler, it may be useful to be able to use either type of coupler on a piece of rolling stock without having to remove anything. It is possible to mount both buffers and chain and knuckle couplers on the same car, provided that one can swing out of the way. Alternatively, either a lug to hold the chain is cast in the body of the coupler or a chain is mounted on top of the coupler. This is also done with an SA3 coupler
SA3 coupler
built by SAB WABCO.[1] Locomotives and some freight cars of the Indian Railways
Indian Railways
are fitted with a 'transition coupler' that incorporates a screw coupling within a knuckle coupler: the knuckle coupler remains in position and does not swing away when not in use. The screw coupling is mounted on a hinge on the opposite side of the knuckle coupler. Most Indian freight cars use the knuckle coupler alone, without buffers, whereas passenger coaches almost exclusively use screw couplers and buffers. Exceptions are the new LHB coaches imported from Europe, and a few other makes of carriages converted to use knuckle couplers.[2][3] Some Russian locomotives and wagons have buffers together with the central coupler. When coupling to Finnish equipment, a short chain with a block that fits in the central coupler is placed on the Russian side, backing up and compressing the buffers so that the chain can be laid on the hook. (That is also the common way of coupling locomotives to or from wagons, faster than unscrewing the link.) British locomotive-hauled passenger carriages adopted a dual coupling system in the 1950s. They have retractable buffers and a central Buckeye automatic knuckle coupler that lowers to reveal a hook for a screw-type chain coupling. When in use, a pin through the buckeye shank rests in the conventional hook. No chain is provided on dual-coupled vehicles, since the chain on the other vehicle can be used when the knuckle coupler is out of the way (down). Inter-stock coupling was with the automatic coupler (with the buffers retracted), while connection to the locomotive was with the buffer-and-chain system with a screw coupler. Today this dual coupling system has been adopted for all loco-hauled passenger trains in Great Britain to allow faster shunting operations.


1 Gallery 2 See also 3 References 4 External links


Coupling adapter for use between Janney coupler
Janney coupler
on a locomotives and WABCO-2 couplers fitted to commuter rail multiple units at New York's Pennsylvania Station. The adapter is seen from the bottom

A Finnish locomotive with dual coupling (SA3 coupler)

Dual coupling
Dual coupling
on a modern locomotive. (Indian locomotive class WAG-9) The chain is mounted on a hinge on the right of the AAR coupler

British-style dual buffer-and-chain/automatic coupler with knuckle swung out of the way

A British Railways Mark 1 coach fitted with a British-style dual buffer-and-chain/automatic coupler with knuckle swung out of the way

JNR Class EF81
JNR Class EF81
the AAR coupler on the right of the Shibata coupler

Bell-and-hook coupler with Willison adapter

Bell-and-hook coupler with Johnston coupler adapter link

Willison coupler adapter for Bell-and-hook couplers

Transition era AAR knuckle coupler. The gap in the knuckle accommodates the link of a link and pin coupler and the vertical hole in the knuckle accommodates the pin.

This locomotive was derailed by the 1906 San Francisco earthquake. The locomotive had three link and pin coupler pockets for moving standard and narrow gauge cars.

See also[edit]

Barrier vehicle Draft gear Knuckle coupler Railway coupling
Railway coupling
by country Railway coupling
Railway coupling
conversion Sets of carriages


^ SAB WABCO C-AK Archived 2009-05-19 at the Wayback Machine. ^ Coupler conversion ^ Centre Buffer Coupler of AAR type

External links[edit]

Adapter piece between Janney coupler
Janney coupler
and Willison coupler

v t e

Railway coupling


Railway coupling
Railway coupling
by country Railway coupling
Railway coupling


Buffers and chain Janney / AAR coupler

Type F & H : Tightlock coupling

SA3 coupler C-AKv coupler Unicoupler/Intermat Scharfenberg coupler Norwegian coupling Dual coupling Drawbar Draft gear